<!DOCTYPE html>
<html lang="zh">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
      span{
          background-color: gray;
          width:100px;
          height: 100px;
          display: inline-block;
      }
      span:after{
            content: ' ';
            border: 35px  solid gray;
            position: absolute;
            left:73px;
            top:23px;
            transform: rotate(45deg);
          /* width:70px;
          height:70px;
          display: inline-block;
          background-color: gray;
          margin-left: 65px;
          margin-top:15px;
          transform: rotate(45deg); */
      }
    </style>
</head>
<body>
    <span></span> 
</body>
</html>